The present invention relates to a picture processing apparatus which can process a plurality of input image picture signals.
A digital copier consists of an image input terminal (IIT) for reading an original document, an image processing system (IPS) for processing resultant picture data, and an image output terminal (IOT) for producing copies based on the picture data by driving, for instance, a laser printer. The IIT picks up, using a CCD sensor, picture information on the original document to produce an analog electrical signal that is in accordance with a reflectivity distribution on the document, and converts it into digital picture data having multi-gradations. The IPS processes the picture data sent from the IIT to perform various corrections, conversions, editing operations, etc. The IOT produces dot pictures by on/off-controlling a laser of the laser printer based on the picture data that has been subjected to the various processes in the IPS.
By virtue of the processes performed in the IPS, this type of digital copier can properly produce pictures in accordance with the kind of picture data having multi-gradations. For example, in the case of characters or the like, edge-enhanced sharp pictures are produced. In the case of half-tone pictures such as photographs, smoothed-out pictures are produced. Further, resolution-adjusted color pictures having high reproduction performance can also be produced. Further, pictures can be produced which have been subjected to various editing operations such as painting, color conversion, trimming, shifting, combining, reduction and enlargement. A color digital copier is constructed such that the IIT provides the IPS with picture data that is produced from color-decomposed signals of the three primary colors of R (red), G (green) and B (blue) while reading the original document, and that the IOT superimposes dot pictures of respective colorants of Y (yellow), M (magenta), C (cyan) and K (black) one on another. A color picture processing apparatus such as the above color digital copier employs individual developers for the above respective colorants, and four scanning operations are performed in accordance with development processes of the respective colorants while at each scanning the original document is read and full color picture data is processed.
Next, the above type of color digital copier is summarized below using, as an example, a configuration that is proposed by the present assignee in, e.g., Japanese Patent Application Unexamined Publication No. Hei. 2-223275 (which corresponds to U.S. patent application Ser. No. 07/482,977).
FIG. 7 shows an example of a configuration of a conventional color digital copier. In FIG. 7, IIT 100 reads a color document using a CCD line sensor to produce color-decomposed signals of the three primary colors of light, B, G and R, and converts those signals into digital picture data. IOT 115 reproduces color pictures by performing laser beam exposure and development. An END (equivalent neutral density) conversion module 101 through an IOT interface 110, that are provided between the IIT 100 and the IOT 115, constitute a processing system of editing the picture data, i.e., an image processing system (IPS), which converts the picture signals of B, G and R into colorant signals of Y, M, C and K, and provides the IOT 115 with the colorant signal that corresponds to the development color in each development cycle.
The IIT 100 reads the document using the CCD line sensor at a resolution of 16 dots/mm for each of B, G and R, and outputs the digital picture data of 24 bits (8 bits.times.3 colors; 8 bits mean 256 gradations). In the CCD sensor, R, G and B filters are mounted on its top surface, and sensor elements are arranged at a density of 16 elements/mm over a length of 300 mm. The CCD sensor performs a sub-scanning operation of 16 lines/mm at a process speed of 190.5 mm/sec. As a result, the reading and data output rate of the image sensor is approximately 15 mega-pixels/sec for each color. In the IIT 100, the reflectivity information is converted into the density information by subjecting the analog signals of B, G and R pixels to a logarithmic conversion, and further the logarithm-converted analog signals are converted into the digital data.
Receiving the color-decomposed signals of B, G and R from the IIT 100, the IPS performs various data processing operations to improve the reproduction performances of color, gradations, resolution, etc., and provides an on/off colorant signal of a development process color to the IOT 115. The END conversion module 101 performs an adjustment (conversion) operation to produce gray-balanced color signals. A color masking module 102 performs an matrix operation on the B, G and R signals to produce signals representing amounts of colorants of Y, M and C. A document size detection module 103 detects the document size in the pre-scanning operation, and performs platen-color elimination (frame erasing) in the scanning operation for reading the document. A color conversion module 104 performs a color conversion operation of a specified color in a specific area determined by an area signal sent from an area picture control module 111. An UCR (under color removal) and black generation module 105 generates a proper amount of K to prevent color impurities and reduce the respective amounts of Y, M and C by an equivalent amount in accordance with the amount of K thus generated. Further, the UCR and black generation module 105 gates the K signal and the under-color-removed Y, M and C signals in accordance with a mono-color-mode signal or a 4-full-color-mode signal. A spatial filter 106 is a nonlinear digital filter having functions of restoring a non-blurred picture and removing a moire phenomenon. To improve the reproduction performance, a TRC (tone reproduction control) module 107 performs density adjustment, contrast adjustment, negative/positive inversion, color balance adjustment, etc. A reduction/enlargement module 108 performs an reduction/enlargement operation in the main scanning direction. The reduction/enlargement in the sub-scanning direction is performed by adjusting the document scanning speed. A screen generator 109 converts the colorant signal of the process color having multi-gradations into an on/off signal (i.e., binary signal) in accordance with its gradation level. The binary colorant signal is provided to the IOT 115 via an IOT interface module 110. The area image control module 111 has an area generation circuit 112 and a switch matrix 113. An editing control module 114 has an area command memory 115, a color pallet video switch circuit 116 and a font buffer 117, etc., and performs a variety of editing control operations.
The area image control module 111 has such a configuration that seven rectangular areas and their priority orders can be set in the area generation circuit 112. Control information for each area is set in the switch matrix 113. The control information includes color conversion information, color mode information indicating one of the mono-color mode, full-color mode and other color modes, modulation selecting information of a photograph, characters, etc., which are used in controlling the color masking module 102, color conversion module 104, UCR and black generation module 105, spatial filter 106 and TRC module 107. The switch matrix 113 can be formed in the form of software.
The editing control module 114 enables a painting operation that is required when a document having a non-rectangular portion, such as a circular graph and a specified area having an arbitrary shape is to be painted a specified color. An area command of 4 bits is written into four plane memories, in which the area command for each point on the document is set by 4 bits of information stored in the plane memories.
In the conventional color digital copier as described above, when a character combining operation is performed, for instance, a certain threshold is established with respect to a character luminance signal, and characters are produced if the character luminance signal is larger than the threshold and an image produced if it is smaller than the threshold.
In the case of combining texture images consisting of structural patterns, for instance, an AC component of a texture image is separated using some boundary value, e.g., its average value paying attention to a luminance signal, and the AC component thus obtained is added to or subtracted from an image. However, this process cannot accommodate a case in which data of two images overlap with each other, such as a perspective combining process.
Therefore, in a perspective combining process of two images stored in a memory, a perspective image is produced by combining two image data alternately read from the memory, as disclosed in Japanese Patent Application Unexamined Publication Nos. Sho. 62-139081 and Sho. 64-23677. Alternatively, a perspective image is produced by taking logical sum of BGR (YMC) image data or determining, on a pixel-by-pixel basis, an average value of two BGR (YMC) data.
However, in the combining method of alternately reading two image data, since the pixel selection is performed with certain regularity, there exist such a problem that a component of a particular frequency existing in a combined image causes defects such as a moire pattern. In the methods of using the logical sum or average value, the combining factors cannot be adjusted in accordance with original images. Further, in the case of using the logical sum, the total density of an image is increased. In the case of using the average value, the BGR or YMC signals depend on characteristics of a filter of the IIT and the colorants of the IOT.